Abnormalities in ribosome function that are implicated in both congenital and acquired bone marrow failure syndromes in humans are classified under the broad umbrella of ribosomopathies. A recent collaboration between our two laboratories has initiated a completely new avenue of research by establishing an evolutionarily conserved role for ribosome modifications mediated by the pseudouridine synthase dyskerin in specific aspects of translation control. The functional role of pseudouridine (?) modifications is of great medical importance as mutations in DKC1, the gene encoding for dyskerin, are found in a number of diseases including X-linked dyskeratosis congenita (X-DC), Hoyeraal-Hreidarsson syndrome, and numerous cancers. Importantly, our published work has identified that the decreased affinity of rRNA ? defective ribosomes for tRNAs results in increased rates of programmed -1 ribosomal frameshifting (-1 PRF), a molecular mechanism that is emerging as an important regulator of gene expression. This proposal seeks to test the hypothesis that global changes in -1 PRF affect the expression of specific subsets of mRNAs encoding key hematopoietic factors, that may contributing to some of the pathological features associated with X- DC. Support for this hypothesis is evident from our extensive published and unpublished findings showing that increased rates of -1 PRF promotes rapid degradation of specific mRNAs through the Nonsense-Mediated mRNA Decay (NMD) pathway. Furthermore, we have demonstrated that rRNA ? levels are impaired in hematopoietic cells from X-DC patients harboring distinct DKC1 mutations. Importantly, our preliminary and published data also suggest that one important functional class of mRNAs involved in telomere maintenance is regulated by this mechanism in both yeast and human cells and is disrupted in X-DC patients, thus linking rRNA ? defects and telomere shortening. By utilizing X-DC as a disease paradigm and combining three model systems, yeast, mouse and humans, in this proposal we will extend our novel findings and identify the repertoire of mRNAs that underlie bone marrow failure associated with ribosome dysfunction and determine the therapeutic potential of inhibiting NMD and -1 PRF in X-DC. Aim 1 of this proposal seeks to identify the repertoire of mRNAs whose expression is affected by rRNA ? defects in yeast, mouse and human cells using two complementary approaches. Aim 2 will determine the mechanisms through which impaired rRNA ? alters expression of -1 PRF containing mRNAs. Aim 3 is oriented towards determining the therapeutic potential of targeting NMD and -1 PRF in X-DC. By the end of the proposed studies, we will have 1) established a new paradigm for understanding ribosomopathies, 2) identified specific genes that can be used as biomarkers and targeted for therapeutic intervention, and 3) explored novel approaches to treat this class of diseases.